path: root/README

Libguestfs is a library for accessing and modifying guest disk images.
Amongst the things this is good for: making batch configuration
changes to guests, getting disk used/free statistics (see also:
virt-df), migrating between virtualization systems (see also:
virt-p2v), performing partial backups, performing partial guest
clones, cloning guests and changing registry/UUID/hostname info, and
much else besides.

Libguestfs uses Linux kernel and qemu code, and can access any type of
guest filesystem that Linux and qemu can, including but not limited
to: ext2/3/4, btrfs, FAT and NTFS, LVM, many different disk partition
schemes, qcow, qcow2, vmdk.

Libguestfs provides ways to enumerate guest storage (eg. partitions,
LVs, what filesystem is in each LV, etc.).  It can also run commands
in the context of the guest.  Also you can access filesystems over FTP.

Libguestfs is a library that can be linked with C and C++ management
programs (or management programs written in OCaml, Perl, Python, Ruby, Java
or Haskell).  You can also use it from shell scripts or the command line.

Libguestfs was written by Richard W.M. Jones (rjones@redhat.com).
For discussion please use the fedora-virt mailing list:

  https://www.redhat.com/mailman/listinfo/fedora-virt


Requirements
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- recent QEMU >= 0.10 with vmchannel support
  http://lists.gnu.org/archive/html/qemu-devel/2009-02/msg01042.html

- febootstrap >= 2.0

- fakeroot

- fakechroot >= 2.9

- XDR, rpcgen (on Linux these are provided by glibc)

- (Optional) Augeas (http://augeas.net/)

- perldoc (pod2man, pod2text) to generate the manual pages and
other documentation.

- (Optional) Readline to have nicer command-line editing in guestfish.

- (Optional) OCaml if you want to rebuild the generated files, and
also to build the OCaml bindings

- (Optional) local Fedora mirror

- (Optional) Perl if you want to build the perl bindings

- (Optional) Python if you want to build the python bindings

- (Optional) Ruby, rake if you want to build the ruby bindings

- (Optional) Java, JNI, jpackage-utils if you want to build the java
bindings

- (Optional) GHC if you want to build the Haskell bindings

Running ./configure will check you have all the requirements installed
on your machine.


Building
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Then make the daemon, library and root filesystem:

  ./configure [--with-mirror=URI]
  make

Use the optional --with-mirror parameter to specify the URI of a local
Fedora mirror.  See the discussion of the MIRROR parameter in the
febootstrap(8) manpage.

Finally run the tests:

  make check

If everything works, you can install the library and tools by running
this command as root:

  make install


Fedora
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We provide packages for Fedora >= 11 in Fedora.  Use those, or build
from our source RPMs - it's far simpler that way.

You can compile libguestfs on Fedora 10 but you cannot use it with the
version of qemu in Fedora 10.  You need to compile your own qemu, see
section 'qemu' below.


RHEL / EPEL / CentOS etc
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We provide packages in EPEL which cover RHEL/CentOS >= 5.  Use those
or build from our source RPMs.


Debian
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libguestfs should build and run on Debian.  At the moment we don't
provide Debian packages, and because of the appliance it's rather
complicated to provide a package which could be accepted into the
Debian repositories.  Want to help?  Please contact us.


qemu
----------------------------------------------------------------------

By far the most common problem is with broken or incompatible
qemu releases.

First of all, you need qemu >= 0.10.4, which contains a vmchannel
implementation.  There are several, conflicting, incompatible things
called 'vmchannel' which at one time or another have been added or
proposed for qemu/KVM.  The _only_ one we support is this one:

  http://lists.gnu.org/archive/html/qemu-devel/2009-02/msg01042.html

Secondly, different versions of qemu have problems booting the
appliance for different reasons.  This varies between versions of
qemu, and Linux distributions which add their own patches.

If you find a problem, you could try using your own qemu built from
source (qemu is very easy to build from source), with a 'qemu
wrapper'.  Qemu wrappers are described in the guestfs(3) manpage.


Note on using KVM
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By default the configure script will look for qemu-kvm (KVM support).
You will need a reasonably recent processor for this to work.  KVM is
much faster than using plain Qemu.

You may also need to enable KVM support for non-root users, by following
these instructions:

  http://www.linux-kvm.org/page/FAQ#How_can_I_use_kvm_with_a_non-privileged_user.3F

On some systems, this will work too:

  chmod o+rw /dev/kvm

On some systems, the chmod will not survive a reboot, and you will
need to make edits to the udev configuration.


Notes on cross-architecture support
----------------------------------------------------------------------

At the moment we basically don't support cross-architecture or
32-on-64.  This limits what is possible for some guests.  Filesystem
operations and FTP export will work fine, but running commands in
guests may not be possible.

To enable this requires work for cross-architecture and 32-on-64
support in febootstrap, fakeroot and fakechroot.

The daemon/ directory contains its own configure script.  This is so
that in future we will be able to cross-compile the daemon.


Mirroring tip
----------------------------------------------------------------------

On my machines I can usually rebuild the appliance in around 3
minutes.  If it takes much longer for you, use a local Fedora mirror
or squid.

To use squid to cache yum downloads, read this first:
https://lists.dulug.duke.edu/pipermail/yum/2006-August/009041.html
(In brief, because yum chooses random mirrors each time, squid doesn't
work very well with default yum configuration.  To get around this,
choose a Fedora mirror which is close to you, set this with
'./configure --with-mirror=[...]', and then proxy the whole lot
through squid by setting http_proxy environment variable).

You will also need to substantially increase the squid configuration
limits:
http://fedoraproject.org/wiki/Using_Mock_to_test_package_builds#Using_Squid_to_Speed_Up_Mock_package_downloads


Porting to other Linux distros / non-Linux
----------------------------------------------------------------------

libguestfs itself should be fairly portable to other Linux
distributions.  Non-Linux ports are trickier, but we will accept
patches if they aren't too invasive.

The main porting issues are with the dependencies needed to build the
appliance.  You will need to find or port the following packages
first:

 - fakeroot
 - fakechroot
 - python
 - rpm-python    http://www.rpm.org/
 - yum           http://yum.baseurl.org/
 - febootstrap   http://et.redhat.com/~rjones/febootstrap/


Copyright and license information
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Copyright (C) 2009 Red Hat Inc.

The library is distributed under the LGPLv2+.  The programs are
distributed under the GPLv2+.  Please see the files COPYING and
COPYING.LIB for full license information.